Studies on the regulation of adenylate cyclase in nucleus caudatus, nucleus accumbens, hippocampus and cerebellar cortex of control and schizophrenic brains were carried out. The adenylate cyclase activity in the dopamine-rich brain areas of schizophrenics was more enhanced by NaF, GTP or GppNHp than in controls. In contrast, these agents stimulated adenylate cyclase in cerebellar cortex and hippocampus of controls and schizophrenics to the same extent. The present results suggest that the regulatory subunit of G/F protein that facilitates adenylate cyclase activation is increased in dopamine-rich brain areas of schizophrenic subjects.